Sharon Benes Professor, Dept. Plant Science CSU Fresno UC-ANR Vegetable Crops Program Team Meeting December 10, 2014; Davis, CA 1
Agricultural Salinity & Drainage Hanson, Grattan & Fulton (2006). Ag & Natural Resources (ANR), Univ. California. Pub. #3375 http://anrcatalog.ucdavis.edu/soilswaterirrigation/ FAO 29: Water Quality for Agriculture Ayars & Westcot (1985). FAO Irrigation & Drainage series www.fao.org/docrep/003/t0234e/t0234e00.htm FAO 48: Use of Saline Waters for Crop Production Rhoades et al. (1992). FAO Irrigation & Drainage Series http://www.fao.org/docrep/t0667e/t0667e00.htm 2
What is salinity? What is sodicity? Salinity units, conversions (and sodicity) Osmotic vs. Specific Ion Effects of salinity Salt tolerance rankings Maas Hoffman tables Salinity Management Leaching fraction (LF) and Leaching requirement (LR) Field Assessment In-situ vs. traditional soil and water sampling 3
Sodium (Na + ) Calcium (Ca 2+ ) Magnesium (Mg 2+ ) Chloride (Cl - ) Sulfate (SO 2-4 ) Bicarbonate (HCO 3- ) Cations Anions Boron (B), Carbonate (CO 3 2- ), Nitrate (NO 3- ), Potassium (K + )
Parent Material of the soil Westside SJV: marine sediments Eastside SJV- granitic materials, not contributing much salinity Irrigation water Imperial Valley Colorado River water has more salt Westside SJV a large volume of low salt canal water applied or now, a lesser volume of more saline well water applied. Fertilizers and amendments Shallow groundwater -------------------------------------------------------------------- Sea spray or seawater intrusion (coastal areas) 5
Total Dissolved Solids (TDS) in ppm (= mg/l) Electrical conductivity (EC) in ds/m (= mmho/cm) Saline soil = EC > 4 ds/m (~ Soil Science Society of America) *Preferred because MH salinity tolerance tables based on ECe. EC = TDS x ~640 (for EC < 5 ds/m) EC = TDS x ~800 (for EC 5 10 ds/m) or for Ca salts EC (drainage waters) = TDS x 740/840/920 for EC s of < 5, 5-10, >10 ds/m, respectively 6
EC w = Electrical conductivity of a water *EC e = EC of saturated soil paste extract EC w X ~1.3 to 1.5* = ECe *depends on soil texture, leaching fraction, frequency of irrigation EC sw = EC of the soil water (nearly twice that of ECe) ECa or EC b = apparent (or bulk) soil conductivity (EM-38 or Veris soil mapping) (Decagon 5TE & Delta-T WET sensors) 7
Ayars & Westcot (FAO 29) 8
Condition of excess of sodium with respect to calcium and magnesium, in the presence or absence of salinity. Soils: measured either as: ESP (exchangeable sodium). condition ESP > 15 = sodic soil SAR (sodium adsorption ratio). SAR > 13 = SAR* = Na + Ca 2+ + Mg 2+ 2 *concs. in meq/l Water: high SAR (> 8-10) 9
Problem for soils. Sodium disperses clays (and O.M.), degrading soil structure and reducing infiltration. Ca 2+ Na + Plant Health: -- Indirect effect: poor aeration and distribution of water. Tough surface crust, hard for seeds to germinate -- Nutritional: negative impact on Ca nutrition. High ph reduces availability of P and cationic micronutrients. 10
San Luis Rio Colorado delta area: saline-sodic, cracking clay soils 11
High SAR (& low EC) water infiltrates poorly 35 30 Severe Reduction in Infiltration Slight to Moderate Reduction in Infiltration Sodium Adsorption Ratio 25 20 15 10 No Reduction in Infiltration 5 Ideal zone 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 EC of Irrigation Water (ds/m) 12
Salinity (ECe) (ds/m) Sodicity (SAR) ph Physical Condition of Soil Non-saline < 4 < 13 < 8.5 Normal Saline > 4 < 13 < 8.5 Normal Salinesodic > 4 > 13 < 8.5 Some degradation Sodic < 4 > 13 > 8.5 Poor Proper management requires proper determination of the soil condition: saline, saline-sodic, or sodic 13
Osmotic effects- more immediate Specific ion effects (Na & Cl-), longer term effect Ion toxicities Nutritional disorders
Salinity effects on plants: osmotic Salinity 15
Strawberry: chloride toxicity 16
Crop choice (MH salinity tolerance tables) Planting position Choice of irrigation water Leaching* Subsurface Drainage* 17
MH Salinity tolerance tables most vegetables - sensitive (S) or - moderately sensitive (MS) 18
pistachio 19
Crop salt tolerance RY = 100% - slope (ECe- threshold ECe) 100 Lower threshold, but low slope Compensates Higher threshold, but higher slope 50 1 2 3 4 5 6 7 8 9 10 Average Rootzone Salinity (ECe) Slide from Steve Grattan, UC Davis Maas and Grattan, 1999
Crop Salt Tolerance in Gypsiferous Soils (may tolerate an ECe substantially higher than their threshold value*) 100 Gypsiferous soils 50 1 2 3 4 5 6 7 8 9 10 Average Rootzone Salinity (ECe) *when preparing the saturated paste, some of the gypsum, not normally soluble, goes into solution, ing the ECe Slide from Steve Grattan, UC Davis.
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Hansen & Grattan (2006), Ag Salinity & Drainage Manual 23
Amount of water applied LF = volume of water that drains below the rootzone / volume of water that infiltrates into the soil But how do we measure this??? Amount of water drained Slide from Steve Grattan, UC Davis
Salinity distribution in relation to various leaching fractions ET Same irrigation water ECw Soil Depth Low LF 40% 30% 20% High LF 10% Slide from Steve Grattan, UC Davis ECe
LR = minimum amount of water, in excess of irrigation requirement, needed to leach salts through a watersaturated soil and ensure proper salt balance. Expressed as the decimal fraction* of the water needed to wet the soil (bring to FC) that must be applied additionally. *So LR is a number between 0 and 1.
1) LR = EC w X 100 (5 X EC e ) EC w = 1.4 X 100 = 0.126 (5 X 2.5) - 1.4 2) Total water needed (AW): AW = ET 1 LR = 90 cm = 103 cm 1 0.126
Assumes that the level of soil salinity is not excessive and does not change very much with time. Objective: apply sufficient water so that soil salinity does not change appreciably with time Source: Ag Salinity Manual, pg. 95
*if salinity affects the crop to the extent that ET is reduced, then just applying the normal crop water requirement may result in some leaching of the profile. 29
Yield Response combined salinity & water stress (Shani et al.,2005. JEQ) Non-stressed condition Salt-stressed condition Water requirement of melons & corn under non-saline irrigation was ~1.0 potential evaporation (E o, Class A Pan) vs. 0.6 E o under saline irrigation 30
Leaching recommendations are being reconsidered. Some experts now feel that we may not have to apply as much as water as the present guidelines suggest. Applying less water for leaching, could help to reduce nitrate leaching. 31
In-situ (real time) measurement Soil vol. water content, EC, temp. sensors (Decagon 5TE, Delta-T WET sensor) Soil solution (suction lysimeters) EM-38 (ECa) Traditional Soil Testing (traditional) Tissue testing Water testing 32
Decagon 5TE Dynamax: Delta-T WET sensor Sensor: ~$250 +datalogger: $500 (direct download) : $1,000 (cellular) Sensor: $1400 (sensor) + ~$700 (datalogger) or kit $2300 (sensor, hand-held meter, cables, software) Accuracy: to 300 ms/m (= 3 ds/m, low!) Measure volumetric water content (VWC), temperature and bulk EC (EC b ; σ b ). Software converts bulk EC to pore water EC (EC p ; σ p which is our EC sw ) Some use the bulk soil EC readings. Others use factory calibrations (mineral vs. organic soil) or their own conversions to get pore water EC. How do we get to saturated paste EC (ECe)? - Not easy: calibrate by taking soil samples and develop an equation to convert EC b (raw readings) to ECe, similar to ground-truthing done for EM-38 soil maps. Advantage: real-time monitoring of salinity in soil Disadvantage: do not have guidelines based on pore water (soil water) EC. Cannnot measure in highly saline soils Readout usually in ms/m. ms/m x.01 = ds/m. 33
Measures bulk or apparent soil EC (EC a ). Ground-truthing: pull soil samples to determine if mapping soil salinity, clay content, other properties or a combination. Convert EC b to EC e 34
Good for assessing degree of spatial variability in soil salinity and where to focus leaching efforts, but if salinity is low in the soil, may also be measuring differences in clay or moisture content. Expensive instrument (>$15,000). Commercial services available. Short rotations: may not be feasible to get frequent readings.. go with traditional soil sampling? 35
Not affected by sodicity 36
Good candidate for gypsum or soil sulfur, if free lime present in the soil 37
Adj EC Ca Mg Na SAR SAR Cl CO 3+ HCO 3 SO 4 B NO 3 -N Fe Mn ph L.I. ds/m meq/l meq/l meq/l meq/l meq/l meq/l mg/l mg/l mg/l mg/l unit Calc RL---> 0.01 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.01 0.1 0.10 0.02 1.0 to 14.0-2.0 to 2.0 SM---> 2510 B 3120 B 3120 B 3120 B Calc Calc 2320 B 3120 B 3120 B 3120 B 4500H B 2330 B EPA---> 300.0 300.0 300.0 001 Ag Wells 0.15 0.74 0.09 0.4 0.6 0.6 <0.1 1.1 0.2 0.02 1.0 <0.10 <0.02 8.2-0.2 General Ag Levels Total Sodium Abs. Ratio Carbonates & Langelier Salts Calcium Magnesium Sodium SAR Adjusted Chloride Bicarbonates Sulfate Boron Nitrate Iron anganese ph Index Low <0.50 <4.00 - - - - - - - - - - - <6.5 < -0.5 Norm al 0.60-1.50 5.00-10.00 1.1-5.0 <4.0 0.1-4.0 0.1-4.0 0.1-1.5 0.1-2.5 0.1-5.0 0.01-0.40 0.1-5.0 <0.20 <0.20 6.8-7.9-0.3-0.5 High for Sensitive Crops 1.51-2.20 > 10.00 > 5.0 4.1-7.0 4.1-9.0 4.1-9.0 1.6-3.5 2.5-3.5-0.41-0.59 5.1-7.0 0.21-0.40 0.21-0.40 8.0-8.4 0.6-0.7 High for Tolerant Crops > 2.20 - - > 7.0 > 9.0 > 9.0 > 3.5 > 3.5 - > 0.60 > 7.0 > 0.40* > 0.40* > 8.4 > 0.9* Notes: Black = Normal Many of the above parameters need specific adjustment for crops, uses, irrigation procedures, etc. Check report for specifics. When sodium is greater than calcium (or high SAR), the w ater is considered sodic or "alkali". Red = High Orange = Sl. High Green = Sl. Low Blue = Low Note: High & Low levels are based on consultant interpretation of the situation, including plant varieties, age, soil type, irrigation system, etc., w hen information is available Sum of cations (or anions) in meq/l 10 = EC (ds/m) Cations = 0.74 + 0.09 + 0.4 = 1.23 1.23/10 = 0.123 38
Salinity is always a concern in irrigated agriculture Drought periods reduce drainage problems.but shift to irrigation with well water or other non-conventional waters can result in higher salinity in the applied water. Drought and irrigation water scarcity will force us to utilize irrigation waters previously deemed unsuitable for irrigation. Ayars and Westcot (FA0 29) guidelines may be too conservative? Tools available for in-situ monitoring, but difficult to relate bulk soil EC (or pore water EC) saturation paste (ECe), the basis of our salinity tolerance rankings. Will have to familiarize ourselves with another set of numbers. 39
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